Application of lead isotope studies to massive sulfide and vein deposits of the Carolina slate belt

Samples of ore leads from a number of Cambrian massive sulfide and vein deposits in the Carolina slate belt of the Charlotte 2 degrees quadrangle, North Carolina, have been analyzed. In general these deposits are characterized by high ²⁰⁷ Pb/ ²⁰⁴ Pb ratios (15.609 to 15.646) and abnormally young model ages (delta [asymp] 100 m.y.). Their thorogenic lead values are typical of those of other deposits of their geologic age. Based on the strong evidence for a syngenetic origin for the massive sulfide deposits, one of two multistage processes is required to explain the data. The first requires derivation of the ore leads from a basement of at least Grenville age and more likely 1.7 to 2.0 b.y. old. Such basement is not known in this portion of the Appalachian Piedmont. We favor the second process which is the derivation of the ore leads from the >10,000 m of felsic, intermediate, and mafic volcanic, volcaniclastic, and epiclastic rocks of the underlying Uhwarrie Formation and Albemarle Group (mean age = 600 m.y.). With an average mu = 25, the model lead ages can be reduced to delta = +20 m.y., assuming a basinal migration of lead at a date of approximately 540 m.y. The vein deposits, using this short-term two-stage model, yield ages of approximately 490 m.y. These correlate well with the peak metamorphism in the North Carolina portion of the Carolina slate belt.